Solubility of water in mixtures of (n-alkanes plus n-perfluoroalkanes) and in n-perfluoroalkylalkanes: experiments and modelling with the SAFT-γ Mie group-contribution approach

The solubility of water in liquid n-perfluorohexane and in an equimolar mixture of n-hexane + n-perfluorohexane is experimentally determined as a function of temperature. The solubility of water in the equimolar mixture is significantly higher than the average of the solubilities in the pure solvents suggesting, for the first time, that mixing hydrogenated and perfluorinated chains enhances the solubility of water. The solubility in the equimolar mixture of n-hexane + n-perfluorohexane is also determined theoretically with the SAFT-gamma Mie group-contribution approach, allowing a direct quantitative estimate of how much the large deviations from ideality contribute to the solubility of water in the mixture. In addition, the SAFT-gamma Mie approach is used to represent the solubility of water in a number of n-perfluoroalkylalkanes, covering a range of relative lengths of the hydrogenated and perfluorinated chains. The theory can be used to predict the relative extent of the solubility of water in the different solvents, in good agreement with the experimental data. This is accomplished by using a single parameter to describe the strong attractive interaction between water and the CH2CF2 group at the junction between the hydrogenated and perfluorinated segments, which is known to be responsible for the increased solubility of water in these substances.